Electric furnaces are widely used for various metal smelting and refining operations. The typical furnace may include a plurality of carbon or graphite electrodes which extend through openings, usually in the roof of the furnace to a location adjacent the level of the melt in the furnace. Typically, the furnace can include several electrodes.
When molten material is tapped from the furnace, the level within the furnace lowers and it is necessary to lower the electrodes to follow the level of the melt in the furnace. Then, when additional charge is added to the furnace, the electrodes must be retraced to maintain them at the proper distace form the melt in the furnace. As the arc from the electrodes smelts or melts the furnace charge, the ends of the electrodes erode. Further, the massive electrodes are constantly lowered and lifted automatically by suitably controlled winches or other drive means to maintain proper operating conditions.
To avoid the escape of hot dust laden and frequently noxious gases with the corresponding environmental hazards and loss of heat and efficiency of the furnace, it is necessary to provide a good seal between each electrode and the furnace as well as between other moveable elements, such as loading chutes, and the furnace. Unless a reasonably gas tight seal is maintained, rapid erosion, and/or oxidation, including necking in or the electrode occurs along that length of the electrode or other moveable which extends through the opening in the furnace roof. Such erosion in the case of an electrode not only weakens the electrode, with the danger that the lower end of the electrode can break off, but also reduces the diameter of the electrode with the result that the current carrying capacity of the electrode is substantially reduced. In addition, the size of any opening between the electrode and the furnace increases as the electrode erodes which allows even more gas to escape. Tests show that typical temperatures of gases when flowing outwardly from a furnace through the annulus between the furnace opening and the electrode are on the order of 3,000.degree. F., and hence, the electrode as well as surrounding structures and equipment can be damaged by the escaping hot gases.
Because of the large current carried by each electrode, the heat of the furnace and the vibration caused by the arc between the end of the electrode and the furnace melt, it is virtually impossible to provide a reliable close fitting seal without danger of damage to the electrode or the roof of the furnace through which the electrode extends. In addition, as a result of conditions within the furnace, the axis of the electrode may tilt slightly which presents further problems with a close fit of the electrode in the furnace opening. Further, there is no known seal material which can withstand the high temperatures between the electrode surface and the furnace roof.
As previously explained, the electrodes are frequently lifted and lowered during operation of the furnace. When the electrode, or other moveable element is lowered, it is also subjected to slag splashing from the furnace. If a close fitting opening or seal is provided at the furnace, slag on the outer surface of the element can damage the seal when the element is withdrawn.
While in many instances the pressure within the furnace is greater than atmospheric, there are times when below atmospheric pressure exists in the furnace. Such conditions may arise where especially noxious gases are emitted by operation of the furnace and such gases must be removed from the furnace by vacuum to avoid operator or worker hazards, and leakage of air into the furnace is usually undesirable.
It is also desirable to maintain the region of the outside of the furnace near the electrode reasonably cool to avoid possible damage to control and manipulating equipment, and to reduce hazards to the workers.
While the electrode seal of application Ser. No. 142,839, is quite durable, satisfactory, and effective, providing the water required for cooling the glands requires piping, flexible hoses, and plumbing which are expensive and space consuming, and disposal of the water used for cooling can be an environment problem.
Consequently, there is a need for a reliable arc furnace seal which seals under conditions of both positive and negative pressures in the furnace, which in no way interferes with adjustment or manipulation of, for example, the electrode, which preferrably requires little or no water cooling, and which requires minimal maintenance. In accordance with this invention, such a seal is provided.